Traditionally, electrical wiring has been installed by electricians one element at a time. In other words, the individual wires were run through the stud walls. These wires were then attached to electrical boxes mounted on studs or other supports such as mounting brackets. The individual electrical components, such as the switches and the outlets were then attached to the wiring in the boxes, and screwed into the box. The drywall would be installed over this, and an opening cut, either before or after installation of the drywall, to allow access to the electrical component.
In order to improve efficiency, factory-prepared, pre-wired assemblies are being utilized. Thus, when a commercial or residential building is wired, the components are pre-assembled in a factory. Such assemblies can include, for example, the electrical components, attached with a drywall ring to a box. Typically, any drywall ears are removed from the electrical component. The box may be attached to a mounting bracket. The actual wire, usually in the form of metal clad or NM cable, is also pre-attached to the box and connected to the electrical component. The electrician attaches the bracket at the appropriate location, runs the cable up through the wall, and attaches it to the next assembly. This greatly reduces the electrician's time, which is a major expense in wiring a building.
The electrical component, either the switch or the duplex outlet, should be flush with the outer surface of the drywall. Typically, the drywall is ⅝-inch to ½-inch thick. However, thicker drywall can be employed. A double thickness of drywall can be used to provide a greater fire rating. In these embodiments, the drywall ring would not place the electrical component flush with the outer surface of the drywall.
To deal with these situations, the electrician must remove the electrical component, insert an electrical box extension, and reinsert the component. The electrical box extension is basically a rectangular sleeve with upper and lower flanges that engage the surface of the drywall. The electrical component is then attached via screws to the drywall ring with the extension between the component and the ring. Tightening the electrical component makes it flush with the outer surface of the drywall. This works, but it requires a great deal of electrician time.
Frequently, the electrical box will not be properly positioned. This can prevent the electrical component from being flush with the drywall, thus creating a possible unsafe condition.